Solar and wind farms that supply power to a utility grid are generally categorized as renewable variable power generation systems. Such systems produce variable power because the harvesting of the solar or wind energy varies with cloud coverage, wind speed, etc. Each solar or wind farm may have a plurality of energy harvesting devices that may require power monitoring and control for coordinating and providing power to the electrical grid. A solar farm, for example, may include multiple photovoltaic cells and associated inverters. A wind farm may include multiple wind turbine generators and associated controllers and converters. Utilities often utilize fossil (coal and gas fired) power plants to stabilize and balance electrical power supplied to the grid, particularly during periods of intermittent sunshine (for solar farms) or during changing wind conditions (for wind farms). Fossil power plants, however, can take a relatively long time to ramp up to full operating power production. Some coal-fired power stations may take hours to ramp up from 0-to-100% of full rated power, and may take even longer to ramp down. However, the power output from the variable renewable energy sources may ramp up or down in a matter of seconds, depending on the available sunshine and wind conditions. Abrupt changes in power output from a source can reduce the frequency regulating ability of a utility grid, and fossil power generation units may have difficulties reducing their power abruptly when a variable plant increases power abruptly. Therefore a need exists to control power ramp rates of renewable variable power generation systems to be more compatible with other types of power generation units that may be limited in their power ramp response rate.
A further need exists for improved systems and methods for controlling power ramp rates in renewable variable power generation systems.